Answer:
Explanation:
Let x is number of books (x ≥0)
Let y is the number of DBA (y≥0)
Given that PB​ = ​$20 and PD​ = ​$40 and  consumer has ​$200 per month, so we can form the inequalities:
200 ≥ 20x+ 40y
So we have a system of  inequalities is:
Please have a look at the attached photo, the right triangle are possible solution for the system.
Hope it will find you well